Reference is initially made to an article entitled "First Production Automotive Capacitive Pressure Sensor" by Gary M. Marks et al which appeared on pages 114 through 117 of the June 1978 issue of Measurements and Control, which describes a transducer pioneered by the assignee of the present invention. The capacitive pressure sensor described in the foregoing article was composed of an alumina (aluminum oxide) diaphragm bonded to a thicker alumina substrate. Both the diaphragm and substrate were circular, and they were bonded together and spaced apart by glass frit, so that the screened conductive layers on their facing surfaces were located in the order of one thousand to a few thousandths of an inch apart. A metal casing was provided to give electrical shielding, and the entire unit was mounted in a plastic housing. The unit has unusually linear response to variations in pressure, and good stability over a wide range of operating temperatures. However, with the demand for increasing numbers of the pressure sensors for use in the more carefully controlled combustion within automobile engines, the cost of each unit is critical and must be minimized.
Accordingly, a principal object of the present invention is to simplify and reduce the cost of pressure sensitive capacitive transducers without sacrificing any precision or reliability.